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UNIVERSITY    OF     ILLINOIS     LIBRARY    AT    URBANA-CHAMPAIGN 


J 


UNIVERSITY  OF  ILLINOIS  BULLETIN 

Vol.  V.  AUGUST,  17,  1908  No.  39c 

[Entered  February  14,  1902,  at  Urbana,  Illinois,  as  second-class  matter 
under  Act  of  Congress  of  July  16th,  1894. 


BULLETIN  No.  9.    DEPARTMENT  OF  CERAMICS 

C.    W.    ROLFE,    Director 


A  CHEAP  ENAMEL  FOR  STONEWARE 

By  R.  T.  STULL 


THE  VISCOSITY  OF  CLAY  SLIPS 

By  A.  V.  BLEININGER 


NOTE  ON  SOME  FUSION  CURVES 

By  A.  V.  BLEININGER 


J  907- J  908 


PUBLISHED   FORTNIGHTLY  By  THE  UNIVERSITY 


A  CHEAP  ENAMEL  FOR  STONEWARE. 

BY 

R.  T.  Stull,  Urbaua,  111. 

The  object  of  this  work  was  to  investioate  some  of  the 
possibilities  of  producing-  a  cheap  enamel,  primarilY  for 
the  improvement  of  the  l)etter  grades  of  stoneware,  and 
secondly,  cheai:>  enamels  for  other  j^urposes  at  temperatures 
lower  than  those  recjuired  for  the  stoneware  industry.  The 
main  object  sought  for  was  an  enamel  which  would  be 
whiter  and  better  than  the  commercial  stoneware  glaze; 
something  on  the  order  of  a  tin  enamel  in  appearance, 
though  much  cheaper. 

Xo  special  field  was  i)lotted  for  investigation.  The 
method  first  adopted  for  carrjing  out  the  work  was  to 
make  up  a  series  of  glazes,  then  select  the  most  promising 
one,  after  firing,  for  the  upper  member  of  the  next  series, 
and  continuing  thus. 

The  method  of  preparing  and  api)lyiug  each  glaze  in 
this  work  Avas  the  same,  so  as  to  obtain  an  accurate  com- 
parison of  results  in  so  far  as  mechanical  and  physical 
application  was  concerned.  The  batch  weight  of  each  glaze 
was  calculated  from  its  respective  formula,  weighed  sep- 
arately, (500  gm.l,  ground  wet  for  two  hours  in  a  small 
porcelain  ball  mill,  passed  through  a  100  mesh  sieve,  placed 
in  a  Mason  jar,  allowed  to  settle  and  the  water  decanted. 
Sufficient  water  was  then  added  in  order  to  ''set''  the  glaze 
at  1.5  B.  »&  L.  hydrometer  (equal  to  about  48  to  52 
Beaume).     Each  glaze  was  then  ready  for  dipping. 

Trials  were  made  from  ready  prepared  stoneware  clay 
from  Monmouth,  111.  A  test  showed  that  the  clay  when 
made  into  slip  form  readily  passed  a  60  mesh  screen  but 
left  quite  a  residue  of  dark  colored  granular  particles  on 
the  100  mesh  screen. 


L      ^ 

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T^ 

gv' 

L. 

^,n^ 

(MR** 

5*-  .-  > 

MM** 

NMM 

^ 

A    CHEAP    ENAMEL    FOR    STONEWARE. 

The  trial  pieces  were 
made  in  the  form  of  small 
"milk"  crocks  3''  across 
the  top  and  li/o''  high. 
These  were  made  in  plaster 
molds  on  a  jigger  and  fin- 
ished outside  on  a  "potter's 
chum." 

The  trials  ^^  ere  dipped 
in  the  bone  dry  condition, 
(Mich  piece  being  immersed 
in  tlie  ghize  al)out  21/0  sec- 
onds. Tlie  dipped  pieces 
were  then  placed  on  a  pot- 
ter's Avheel,  the  glaze 
turned  off  from  the  rim 
and  shoulder  and  the 
pieces  nested  in  "fives"  for 
setting  in  saggers. 

In  order  to  determine 

the    relative    fusibility    of 

the  glazes,  cones  were  made  from  each  mixture  and  the 

bending  points  or  softening  temperatures  determined  by 

Seger  cones  and  the  Le  Chatelier  pyrometer. 

All  the  glazes  in  this  work  were  fired  in  the  down-draft 
open  fire  kiln  of  the  ceramic  department  at  the  University 
of  Illinois.  Series  I  was  fired  to  cone  6  in  12  hours,  coke 
being  the  fuel  used. 

For  the  starting  point  of  this  work,  a  glaze  having  the 
following  formula*  was  selected  : 


Trial   pieces  nested  in   "Fives"  ready 
for  the  Sagger. 


No.  I,  Series  I 


•  3  K.0 
.4  CaO 
.3  BaO 


•  4  ALO.,      3-75  SiO. 


This  formula  produces  a  clear  bright  glaze  having  a 
range  of  temperature  from  cone  4  to  cone  8,  within  which 
it  is  a  good  glaze. 


*Sprechsaal ;  1905,  No.  42. 


A    CHEAP    ENAMEL    FOR    STONEWARE. 


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fa  A    CHEAP     ENAMEL    FOR     STONEWARE.      ' 

The  first  series  was  made  for  the  piiiijose  of  determin- 
ing the  relative  fusibility,  brilliancy  and  opacity  induced 
by  BaO  as  against  ZnO,  by  gradual  replacement.  The 
formuhne  and  batch  weights  of  series  I  are : 

Appearance  of  Trials. 

The  softening  temperatures  expressed  in  degrees 
centigrade  are  given  in  the  column  at  the  right  of  percen- 
tage batch  weights  above.  When  taken  from  the  kiln,  all 
five  glazes  were  well  matured,  and  showed  no  bad  defects. 
After  two  days'  time  crazing  began  to  appear  in  all  glazes 
except  No.  5.  Crazing  was  worst  in  No.  1,  gradually  de- 
creasing toward  No.  5,  which  was  free  from  crazing. 

No.  5  is  the  most  fusible  glaze  in  the  series  and  has 
the  best  brilliancy  and  opacity;  opacity  not  very  great. 

SERIES  II. 

No.  5  from  series  I  being  the  best  glaze,  was  selected 
for  the  starting  point  of  Series  II,  in  which  the  CaO  from 
whiting  was  gradually  replaced  by  CaO  from  bone  ash,  all 
other  members  remaining  constant.  This,  of  course,  in- 
creased the  acidity  by  the  amount  of  P2O5  brought  in  with 
tiie  bone  ash. 

After  series  II  was  made,  it  was  thought  lliat  the  use 
of  raw  bone  ash  might  cause  defects  such  as  blistering  and 
curdling,  consequently  series  III  was  made,  keeping  the 
same  formulae  as  in  series  II  but  having  the  bone  ash  cal- 
cined with  flint.     This  calcine  was  marked  "A." 

Calcine  A  Formula  :  Percent  Batch  Weights  : 

1.  OaO,     1.  SiO.,      1/3  PsO.,         Bwft    i¥h    63 .  19 

Combining    weight    I631X5.         Flint    36 . 81 

This  mix  gave  a  friable  mass  when  burned  to  cone  6. 


A    CHEAP    EXAi!EL    FOR    STONEWARE. 


SERIES  III. 
Percentage  Batch  Weights. 


'C. 


o  r- 


No.  6A 
No.  7A 
No.  8A 
No.  9A 


46.09 

8.28 

4-50 

6.70 

7.12 

27.31 

46.05 

5-51 

9.00 

6.70 

7. II 

25.63 

46.01 

2.75 

13.50 

6.69 

7.10 

23.95 

45-97 

17.97 

6.68 

7.10 

22.28 

1160° 

1200° 
1230° 
1250° 


All  j^lazes  except  No.  5  in  series  II  flaked  off  after 
dipping.  If  the  trial  pieces  were  jarred  after  drying,  the 
glazes  shelled  off  leaving  the  trials  bare.  None  of  the  trials 
in  series  III  showed  signs  of  flaking  after  dipping. 

In  order  to  test  the  relative  effects  of  raw  and  calcined 
bone  ash,  3%  of  dextrine  was  added  to  glazes  6,  7,  8  and  9 
of  series  II  after  which  they  dipped  very  nicely,  giving  no 
trouble  in  flaking  when  dry,  but  later  flaked  some  during 
burning. 

Glazes  from  series  II  and  III  were  placed  in  saggers 
and  fired  to  cone  6  in  11  hours. 


Appearance  of  Triah. 

There  is  no  appreciable  difference  in  fusibilitj'  between 
those  glazes  which  contained  raw  bone  ash  and  the  corres- 
onding  ones  in  which  it  had  been  calcined  with  flint. 

Glazes  No.  5,  6  and  7  of  series  II  and  6A  and  7A  of 
series  III  were  matured;  Nos.  8  and  9,  8A  and  9A  were 
dull  in  appearance  due  to  insufficient  Temperature  to 
mature  them. 

Since  the  members  in  the  two  series  highest  in  bone 
ash  were  immature,  it  was  decided  to  make  a  second  firing 
of  series  II  and  III  to  cone  8.  The  trials  were  set  and  the 
kiln  finished  in  14  hours.  On  opening  the  kiln,  the  cones 
showed  evidence  of  a  much  higher  temperature  than  cone 


8  A    CHEAP    ENAMEL    FOR    STONEWARE. 

8,  probably  cone  9  at  least.  All  the  softer  glazes  showed 
evidence  of  overtiring,  showing  a  sort  of  -'pitted"  or  egg-, 
shell  surface.  8  and  8A,  9  and  9A  were  nicely  matured. 
No  blistering  or  serious  crawling  occurred.  Nos.  9  and  9A 
were  whitest,  whiteness  decreasing  toward  No.  5.  Nos.  9 
and  9A  were  crazed  in  fine  meshes,  the  crazing  gradually 
decreasing  toAvard  No.  5. 

SERIES  IV. 

No.  9A  is  the  best  as  to  working  qualities  and  white- 
ness, though  crazed  and  too  refractory  for  the  best  develop- 
ment of  the  stoneware  body  used.  This  glaze  was  selected 
for  the  upper  members  of  series  IV.  The  object  undertaken 
was  to  ''soften  down"  9A  and  at  the  same  time  overcome 
the  crazing  and  retain  as  much  of  its  whiteness  as  possible. 

In  order  to  do  this  the  most  promising  method  seemed 
to  be  to  introduce  B2O3  in  the  form  of  calcium  borate.  By 
replacing  part  of  the  SiOa  with  B.^,,  ^^^^  softening  of  the 
glaze  and  the  overcoming  of  crazing  might  be  accomplished. 
The  introduction  of  calcium  borate  was  looked  upon  as  a 
possibility  for  retaining  the  whiteness,  since  it  sometimes 
produces  opalescence  in  glazes. 

In  order  to  save  the  time  and  trouble  of  making  a  fritt, 
the  naturally  occurring  mineral  "Colemanite"  was  used. 
This  is  the  mineral  from  which  our  borax  and  boracic  acid 
is  largely  obtained.  Its  formula  is  2  OaO,  3  B2O3,  5  HoO. 
Molecular  wt.=412.  Combining  wt.  1.  RO=206.  Accord- 
ing to  Dana*  colemanite  crystallizes  in  the  monoclinic 
system,  usually  in  short  prisms.  Cleavable,  b-highly  per- 
fect;  c — distinct.  Before  the  blowpipe;  decrepitates,  ex- 
foliates, sinters  and  fuses  imperfectly. 

Series  IV  was  produced  by  gradually  replacing  part 
SiOo  in  glaze  No.  9 A,  .2  equivalents  at  a  time,  by  BoOo  in 
the  form  of  colemanite,  up  to  1.0  equivalent  of  B2O3.  By 
introducing  1.0  B2O3  as  colemanite,  .6%  OaO  was  carried 
in.  This  replaced  .3  ZnO  and  .3%  CaO  from  bone  ash, 
giving  glaze  No.  14  in  the  table  below : 


*A  Text  Book  of  Mineralogy,  pp.  519,  520. 


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10  A    CHEAP     ENAMEL    FOR     STONEWARE. 

The  trials,  and  cones  made  from  the  glazes  for  the 
fusibility  test,  were  set  in  the  kiln  in  the  same  manner  as 
in  the  previous  burns.  Before  a  dull  red  heat  was  reached, 
all  the  cones  made  from  those  glazes  containing  colemanite 
crumbled  to  a  fine  powder  on  the  placque.  No.  9A,  contain- 
ing no  colemanite,  remained  standing.  Powdered  colema- 
nite dehydrates  at  a  very  low  heat,  swelling  to  nearly  twice 
its  original  volume  without  softening,  which  accounts  for 
the  "falling  to  ]3owder''  of  the  cones  made  from  those  glazes 
in  which  colemanite  was  present. 

The  first  intention  was  to  fire  the  trials  to  cone  6. 
From  the  behavior  of  the  cones  it  was  assumed  that  the 
colemanite  glazes  would  crumble  from  the  trials,  hence  the 
kiln  was  finished  at  cone  8  in  order  to  mature  No.  9A. 

Appearance  of  the  Trials. 

No.  9A  softened  at  1250°C  the  same  as  in  the  previous 
burn,  going  down  with  cone  6.  It  was  impossible  to  deter- 
mine the  softening  points  of  the  other  members  of  this 
series  since  their  cones  crumbled  to  powder  in  the  early 
stage  of  the  burning. 

No.  9A  matured  nicely,  is  a  little  whiter  than  in  the 
previous  burn. 

Nos.  10,  11,  12,  13  and  11  crumbled  off  from  the  out- 
sides  of  the  crocks  leaving  them  bare,  and  fell  to  the  bottom 
on  the  insides,  fusing  in  thick  layers.  No  accurate  conclu- 
sions could  be  drawn  from  these  except  -that  they  were 
much  more  fusible  than  No.  9 A  and  overfired. 

This  is  as  far  as  the  work  has  been  carried.  The  next 
step  will  be  to  make  a  series  in  which  the  colemanite  has 
been  dehydrated  after  the  same  formulae  as  those  in  series 
IV. 

According  to  the  composition  and  low  temperature  of 
fusion  of  colemanite,  it  is  undoubtedly  a  valuable  flux  for 
the  introduction  of  BoOg  in  an  insoluble  form.  If  it  can 
be  had  in  a  reasonable  state  of  purity  in  suflftcient  quanti- 
ties, and  at  a  moderate  price,  a  large  portion  of  the  trouble 


A    CHEAP    ENAMEL     FOR     STONEWARE. 


">        sa       S 

CT»  O)  O) 


3avy*)llK/30     933^030 


12  A    CHEAP    ENAMEL    FOR    STONEWARE. 

and  expense  of  fritting  can  be  eliminated.  It  will  also  be 
valuable  in  simplifying  the  leadless  glaze  problem,  as  well 
as  a  valuable  Hux  for  hardening  terra  cotta  slips  for  low 
fire  work. 

DISCUSSION. 

Mr.  Purdy :  I  will  ask  Mr.  Stull  two  questions.  One 
is  as  to  the  calcium  phosphate.  We  known  that  increased 
whiteness  and  opacity  of  the  glaze  can  be  secured  by  use 
of  bone  ash,  but  can  you  use  it  to  any  great  extent  without 
having  crawling? 

Mr.  HtuU:  I  have  not  experimented  extensively  in 
using  bone  ash  for  a  glaze  ingredient,  but  here  used  .4  CaO 
as  bone  ash  and  there  was  no  evidence  of  crawling. 
Whether  more  could  be  used,  I  do  not  know.  It  materially 
increases  the  temperature  necessary  to  mature  it. 

Mr.  Furdjj :  Bone  ash,  according  to  my  experience,  is 
a  very  dangerous  substance  to  use  in  a  glaze  of  that  kind. 
Another  question  I  will  ask,  in  harmony  with  Prof.  Binns' 
paper;  does  BoO.-j  tend  to  increase  the  opacity  of  the  glaze? 
Are  vou  getting  a  whiter  glaze  with  increased  content  of 
B2O3? 

Mr.  Stnll :  I  believe  it  depends  on  the  composition  of 
the  glaze  whether  it  imparts  whiteness  or  not.  In  itself,  I 
do  not  believe  it  does.  But  colemanite  is  borate  of  lime, 
practically  insoluble  when  cold,  though  it  fuses  by  itself 
at  a  low  heat,  and  the  theory  is  advanced  that  whiteness 
can  be  obtained  by  incorporating  calcium  borate  into  the 
glaze,  which  precipitates  or  segregates  within  the  glaze. 
That  is  what  I  intend  to  follow  out.  The  line  of  inquiry 
will  be  changed  from  time  to  time  as  results  from  the  kiln 
warrant.  I  do  not  believe  that  B2O3  can  take  the  place  of 
AlgO-j,  or  that  it  will  act  as  ALOo  does.  In  nature,  in  all 
the  boracic  acid  minerals,  BoO-;  takes  tlie  part  of  an  acid. 

Mr.  Humphreys :  I  will  ask  Mr.  Stull  what  form  of 
whiting  he  used.  I  think  that  is  important  in  comparing 
with  bone  ash  for  temperature.     In   some  recent  experi- 


A    CHEAP     ENAMKL     lOR     STONEWARE.  13 

meuts  I  found  as  much  as  a  dittereuce  of  two  cones  in  the 
different  whitings. 

Mr.  l^titU:  I  am  not  prepared  to  say  where  it  was 
obtained.     1  found  it  in  the  laboratory  there. 

Mr.  Piirdi/:  The  whiting  was  ordered  from  the  Illi- 
nois Supply  Co.,  East  St.  Louis. 

Mr.  Mayer:  Mr.  President,  I  was  not  present  when 
all  the  paper  was  read,  but  I  heard  him  mention  colemanite. 
I  made  some  experiments  with  some  colemanite,  the  analy- 
sis of  which  was : 

B2O,    54.80 

CaO   29.50 

H2O    13.50 

Carbonate  .K:  Sulphate  of  Lime  and 

Silica    2.00 


99.80 


The  experinsents  were  made  with  a  raw  glaze  of  ex- 
actly the  same  composition  of  the  fritted  glaze  we  were 
using  right  along.  The  note  I  made  was,  ''good  glaze,  ap- 
parently as  good,  as  brilliant  as  the  ordinary  glaze,  suits 
colors  as  well  as  our  regular  glaze."  It  was  much  better 
color  than  our  own  glaze.  I  have  experimented  largely 
with  different  forms  of  colemanite.  There  is  only  one  dis- 
couraging feature  and  that  is  we  cannot  buy  it  cheaper 
than  borax  and  boracic  acid.  Did  Mr.  Stull  ask  the  price 
of  this  colemanite?  I  found  that  the  trouble.  We  could 
get  any  amount  of  it  and  extremely  pure,  very  little  im- 
purity in  it — white  as  snow;  but  they  want  an  unearthly 
price  for  it.  1  did  not  get  mine  from  the  Pacific  Coast 
Borax  Co.  I  got  it  from  a  firm  that  had  just  found  some 
deposits  of  extreme  purit^v.  The  only  trouble  is  the  high 
price  the  people  want  for  it.  In  practice  they  make  glazes 
identically  the  same.  I  have  not  seen  any  peculiarity 
about  it. 

Mr.  Binns:  I  will  ask  Mr.  Mayer  if  he  dehydrated 
the  colemanite? 


14  A    CHEAP     ENAMEL    FOR     STONEWARE. 

Mr.  Maijer:  1  just  used  the  colemanite  as  it  comes 
from  the  mines. 

3Ir.  Bijuis :  And  you  did  not  experience  the  trouble 
Mr.  Stull  had  on  account  of  the  pulverizing  of  the  glaze? 

Mr.  Mayer:  I  never  had  any  such  experience,  and  1 
used  colemanite  from  three  different  firms.  The  last  one  I 
experimented  Avith  was  an  extremely  pure  sample.  I  never 
saw  that  difficulty  in  any  of  them.  It  is  extremely  hard, 
very  difficult  to  grind.  I  broke  several  mortars  before  I 
learned  how  to  break  it  up. 

Mr.  Bill  IIS  :  Although  not  germane  to  this  discussion, 
Mr.  Chairman,  I  want  to  speak  concerning  Mr.  Stull's  last 
statement.  In  mineralogy'  there  is  one  case  of  boron  as  a 
base,  as  I  said  yesterday.  Datolite  is  a  silicate  of  boron 
and  calcium.  The  claim  which  I  made  yesterday  was  for 
boron  in  the  presence  of  silica,  which  must  not  be  ignored. 
I  granted  that  boron  acted  as  an  acid  in  the  presence  of 
bases. 

I  am  interested  in  Mr.  Stull's  optimism  when  he 
thinks  the  difficulty  of  leadless  glazes  may  be  solved  by  the 
use  of  colemanite.  T  do  not  think  the  difficulty  of  a  leadless 
glaze  lies  in  the  expense  of  fritting,  rather  in  the  manipula- 
tion of  the  process.  I  am  interested  in  the  development  of 
the  use  of  bone  ash,  and  there  are  one  or  two  points  which 
seem  to  me  need  more  light.  My  experience  has  been 
rather  on  the  line  of  Mr.  Purdy's',  that  bone  ash  is  danger- 
ous to  use.  If  intended  to  be  used  on  a  large  scale,  on  a 
large  mass  of  ware,  that  is  where  the  trouble  would  come  in. 

I  will  ask  Mr.  Stull  in  that  connection  what  his  ex- 
perience was  in  calcining  bone  ash  with  flint ;  to  what  tem- 
perature he  took  it ;  what  he  tried  to  accomplish,  and  if  he 
thinks  he  accomplished  his  purpose? 

Mr.  Stull :  Answering  Mr.  Mayer's  question,  these 
experiments  were  carried  out  on  the  strength  of  the  new 
deposit  which  has  been  discovered,  and  I  am  told  that  the 
Pacific  Coast  Borax  Co.  have  carloads  of  it.  The  represen- 
tative of  this  company  said,  in  answer  to  a  question,  that 
they  could  furnish  it,  but  I  do  not  know  at  what  price.     I 


A    CHEAP    ENAMEL     FOR     STONEWARE.  16 

have  not  gotten  the  price  yet.  As  I  stated,  we  will  have  to 
investigate  the  matter  of  price. 

The  mineral  which  Mr.  Mayer  speaks  of  as  colemanite 
is  not  colemanite,  but  j)artially  dehydrated  colemanite.  It 
is  of  the  same  composition  as  colmanite  except  that  it  is 
l)artiall3'  dehydrated.  There  is  a  deposit  in  Oregon  of  this 
dehydrated  colemanite.  That,  of  course,  being  partly  dehy- 
drated would  not  decrejjitate  and  would  not  give  the 
trouble  I  experienced  with  colemanite,  the  trouble  of  the 
true  mineral  colemanite  which  contains  21.90%  HoO. 

Keplying  to  Mr.  Binns'  inquiry  in  regard  to  the  use  of 
bone  ash,  my  experience  is  limited  to  this  case.  I  had  no 
trouble  at  all.  I  made  three  burns,  six,  eight  and  nine, 
and  in  no  case  did  I  run  into  blistering.  The  great  diffi- 
culty I  had  with  the  raw  bone  ash  was  that  it  flaked  off 
badly.  It  fell  off  by  itself  in  the  drying.  The  idea  of  cal- 
cining it  with  flint  was  that  in  the  manufacture  of  bone 
china  it  is  often  found  necessary  to  recalcine  bone  ash  to 
prevent  blistering,  etc.,  and  I  thought  it  best  to  recalcine 
it  with  a  little  flint  and  grind  it  and  use  it  in  that  form. 
There  was  no  special  reason  except  to  get  a  soft  mass — not 
to  burn  too  hard,  though  it  would  not  harden  by  itself. 

Mr.  Binns :  I  was  born  and  raised  on  bone  china  and 
that  is  news  to  me.  The  calcining  of  feldspar,  without 
producing  any  chemical  change  produces  a  physical 
change;  but  I  did  not  see  how  the  calcining  of  bone  ash 
could  have  any  effect,  as  it  has  already  been  calcined. 

Mr.  ^StaU :  I  do  not  know  anything  about  bone  china, 
never  saw  it  made ;  and  as  I  said,  my  only  experience  in  the 
use  of  bone  ash  was  in  this  case.  Professor  Bleininger  sug- 
gested calcining  it  for  that  reason,  and  I  think  the  German 
literature  has  something  about  the  calcining  of  bone  ash 
as  obtained  from  the  dealer,  and  gives  instances  where  the 
trouble  was  overcome  by  recalcining. 

Mr.  Mayer:  Mr.  Stull  says  the  colemanite  I  got  was 
not  colemanite.  I  am  not  a  mineralogist  and  do  not  pretend 
to  know  about  these  things,  but  I  give  you  the  name  they 
call  it.     The}^  sometimes  call  it  "pandermite''  and  some- 


16  A    CHEAP    ENAMEL    FOR    STONEWARE. 

times  colenianite.  I  caimot  tell  the  difference.  I  know  it 
had  13.50%  water  in  it.  That  I  will  vouch  for.  I  think 
the  man  Avho  gave  me  the  sample  is  as  much  of  a  mineralo- 
gist as  I  am,  and  he  sometimes  calls  it  pandermite  and 
sometimes  colenianite.  But  it  gave  excellent  results.  The 
price  nmde  it  simply  out  of  the  question  to  use. 

Air.  BJeiiiinger:  The  main  object  of  Mr.  Stull's  ex- 
periments is  twofold, — one  practical  and  one  more  theo- 
retical. The  practical  object  is  to  obtain  a  cheap  stoneware 
glaze  for  a  certain  type  of  stoneware.  The  second  is  to 
make  large  and  extensive  experiments  which  will  tend  to 
shoAv  the  various  opacifying  agents.  Therefore,  he  has 
undertaken  the  work  to  show  how  the  various  opacifying 
agents  behave  and  produce  workable  glazes. 

Mr.  Bbins :  Tf  Mr.  Mayer's  glazing  was  done  on  bis- 
cuit ware  and  Mr.  Stull's  on  green  ware,  it  may  be  i30ssible 
that  the  combined  water  in  the  clay  may  have  caused  de- 
crepitation. 

Mr.  Still] :  It  occurred  before  the  kiln  was  red  enough 
to  see  the  cone.  May  I  ask  Mr.  Mayer  what  percent  of 
water  was  in  the  dehydrated  colemanite  he  used? 

Mr.  Mayer:  The  composition  of  the  glaze  in  which  1 
used  this  colemanite  was : 

Feldspar    271 . 7 

White  Lead  105 . 0 

Florida  Clay 59.2 

Colmanite    150.0 

Whiting 44.8 

Flint 139.6 

Mr.  StuU:  In  pure  colmanite  there  is  21.90%  HoO. 
I  will  ask  Mr.  Mayer  what  was  the  percent  of  water  in  his 
variety? 

Mr.  Mayer:     13.50  of  water. 

Mr.  StuU:  It  was  probably  half  way  between  hy- 
drated  and  dehvdrated  colmanite. 


A    CHEAP    ENAMEL    FOR    STONEWARE.  17 

*COXTIXUATIOX  OF  THE  WORK. 

The  next  step  decided  upon  was  to  make  up  several 
glazes  represeutiug  five  different  series,  determine  their 
softening  temperatures  in  the  form  of  cones,  group  these 
glazes  according. to  their  softening  temperatures  and  fire 
them  accordingly. 

8ince  the  glazes  in  series  IV  in  which  raw  colemanite 
was  used  powdered  from  the  trial  pieces,  series  V  was  made 
according  to  the  respective  formulae  in  series  IV,  the  only 
difference  being  that  the  colemanite  was  dehydrated. 

^EKIE8  VI,  VII  AND  VIII. 

These  series  were  constructed  for  the  uprpose  of  de- 
termining the  effect  of  increasing  AI0O3  and  PoO.^  by  the 
use  of  aluminum  pliosphate  in  the  presence  of  calcined 
bone  ash  and  B2O3. 

Since  the  sample  of  colemanite  at  hand  was  exhausted 
in  making  series  V,  and  since  letters  to  two  borax  compan- 
ies brought  replies  that  they  had  no  colemanite  for  sale  as 
it  was  all  absorbed  by  their  plants  in  the  refining  of  borax 
and  boracic  acid,  it  was  decided  to  make  a  fritt  after  the 
dehydrated  colemanite  formula  for  use  in  the  three  follow- 
ing series.    This  was  designated  "Fritt  B." 

Fritt  B.  Batch  Weights : 

Formula  Whiting    50 

2  CaO,  3  B0O3  Boracic  Acid 93 

A  preliminary  test  in  the  Pelton  electric  furnace 
shows  that  this  mixture  swells  at  700° C  to  a  porous  sponge- 
like mass  and  melts  to  a  clear,  water-like  fluid  at  950°C. 
An  attempt  to  make  a  drop  fritt  of  this  mixture  had  to  be 
abandoned  on  accoutn  of  its  great  fluidity  and  corrosive 
action.     It  soaked  through  the  fire  clay  crucible,  draining 


*This  installment  represents  the  work  which  has  been  done  on  "A 
Cheap  Enamel  for  Stoneware,"  between  the  last  convention  and  the  date 
of  publication. 


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A    CHEAP    ENAMEL    FOR    STONEWARE. 


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20  A    CHEAP    ENAilEL    FOR    STONEWARE. 

out  at  the  bottom  like  water  through  a  sponge,  and  in  a 
short  time  dissolved  the  bottom  from  the  crucible  com- 
l^letely.  In  order  to  increase  viscosity  and  reduce  corrosive 
action,  ''fritt  C"  was  constructed  having  the  formula : 

FRITT   C,  BATCH  WEIGHTS. 

.3  KoO         )  (1.8  SiOs  Brandy  wine    Feldspar    46.26 

[   .3  Al:03  ]  i.o  B,03  Whiting    18.46 

.7  CaO         j  {     .011   P2O,  Flaky  Boracic  x\cid   34.33 

^      ,.   .  .  ,, ^  Bone  Ash   95 

Combming     weight — 277.6 

This  mixture  gave  a  very  satisfactory  drop  fritt,  very 
white  and  translucent.  This  fritt  was  used  in  making  the 
three  following  series : 

SERIES  IX. 

In  this  series  the  RO  and  acid  were  kept  constant  in 
order  to  note  the  effect  of  increasing  the  AUOo  by  using 
calcined  Georgia  kaolin.  The  glaze  selected  for  the  lirst 
member  in  this  series  has  the  formula : 

No.  30        .2  K2O)  i2.5  Si02 

2  ZnO\       .4  ALO3  .2  P2O5 

.6  CaO)  /    .8  B2O3 

A  trial  fritt  marked  "Fritt  D"  composed  of  bone  ash, 
whiting  and  boracic  acid  was  tested.  Its  formula  and 
batch  weights  are: 

FRITT  D. 
Formula.  Batch    Weight.s. 

pp.  Bone   Ash    28.94 

I .  CaO        I  /;^  ,^:'^A  n  Whiting   9.34 

U.33  1-3  i3,U3  pij^j^y  Boracic  Acid 61.72 

A  portion  of  this  mix  when  tested  in  the  Pelton  fur- 
nace softened  at  760° C  and  fused  to  a  thick  viscous  paste 
at  11G5°C.  On  testing  for  solubility  in  hot  water,  it  was 
found  that  the  B2O3  dissolved  readily,  leaving  a  fine  white 
paste  of  bone  ash  and  calcium  borate.  This  shows  the 
stability  of  bone  ash  in  the  presence  of  B2O3,  since  no 


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22  A    CHEAP    ENAMEI,    POR     STONEWARE. 

chemical  arrangement  took  place,  except  the  formation  of 
calcium  borate  with  the  free  CaO  from  whiting. 

On  account  of  its  solubility,  fritt  D  could  not  be  used. 
Instead,  fritt  E  was  made. 

FRITT  E. 
Formula. 
.262-3  K2O    )  I  1.6  Si02 

.60        CaO     L262-3  AUOa       .2  P0O5 
.131-3  ZnO    i  (  1.062-3  B.O3 


Cmbining  weight— 295.733 


Batch   Weights. 


Brandy  wine   Feldspar    42.01 

Bone  Ash    17-53 

Zinc  Oxide   3 .  05 

Flaky  Boracic  Acid   37-41 

This  mixtiiie  makes  a  beautiful  drop  fritt ;  white  and 
opaque,  resembling  a  tin  fritt  in  appearance,  and  is  prac- 
tically insoluble. 

The  softening  temperatures  of  all  the  glazes  in  series 
Y,  VI,  VII,  VIII  and  IX  were  determined  by  the  Le 
Chatelier  pyrometer  in  the  Pelton  furnace,  the  softening 
points  of  each  series  being  determined  separately.  These 
glazes  were  then  arranged  according  to  their  bending  tem- 
peratures for  burning.  No.  14c  being  softest  and  No.  19  the 
most  refractory.  As  arranged  in  the  table,  all  glazes 
softening  between  950 °C  and  1027 °C  were  fired  at  cones 
03  and  01.  Those  softening  between  1027° C  and  1120° G 
were  burned  at  cone  2,  while  those  bending  between  1033 °C 
and  1161  °C  were  fired  at  cones  1  and  6. 

Leu  gill  of  Time  of  Buriiiuf/. 

Cone  03  was  made  in  9  hours. 
Cone  01  was  made  in  11  hours. 
Cone  2  was  made  in  18  hours. 
Cone  4  was  made  in  17  hours. 
Cone  6  was  made  in  19  hours. 
Coke  being  used  as  fuel. 


A    CHEAP    ENAMEL    FOR    STONEWARE.  23 

Glaze  °C 

No.  14c    953^ 

No.  25    952 

No.  26    967 

No.  31    976 

No.  27    980] 

No.  30    991/ 

No.  14X     99-^ 

No.  32    996\         Fired  at 

No.  I2C    1000 ,  Cones  03  &  01 

Mo.  S3    1001 

No.  20    ioio\ 

No.  35    loir 

No.  21    1025 

No.  34 1026 

No.  12X    1027 

No.  13X    1027^ 

No.  22    1033    / 

No.  28    1 040 1  I 

No.  29    1050  I  V       Fired  at 

No.  23    1070/  /  Cone  2 

No.  iiX     1077'  I 

g"-24    1090'    \      pi,,j  ,t 

No.  IOC   ii20i  ;         /^^„„^   .  p  K 

No.  loX     1120,    /  ^°"'^  4&  6 

No.  16    ii37\ 

No.  17    1155] 

No.  15    1145I 

No.  18    11551 

No.  19    1161/ 

In  each  cnse  after  firiiiii'  was  finished,  (he  fire  was 
drawn,  tlie  fii'e  box  door  and  damper  left  open  and  the  kiln 
allowed  to  cool  quickly. 

Ari'EAKANCE  OF  THE  TKIAL^. 

Series  V. 

No.    lOX.     Cone  '2:      White,  smooth,   no  l)eadin<^-;   imder- 

fired. 

Cone  4 — (,>aite  white  and  opaipie,  slightly  beaded, 
crazed  some. 

Cone  6 — Opalescent,  blisters  where  thick,  crazed.  No 
beading. 


No.  11 X.     Cone  2:     Opalescent,  crazed,  otherwise  a  good 
glaze. 


24  A    CHEAP    ENAMEL    FOR    STONEWARE. 

Cone  4 — A  good  clear  bright  glaze.  Opalescent  where 
thick,  no  crazing. 

Cone  6 — Appearance  same  as  at  cone  4  except  runs 
more. 


No.   12X.     Cone  03 :     Glaze  somewhat  immature,  smooth. 

Cone  01— Bright     and     opalescent,     slightly     beads, 
crazed. 

Cone  2 — Bi-ight,  less  opalescent,  smooth,  no  crazing. 


No.  13X.     Cone  03  :     Underfired,  matt. 

Cone  01 — Bright,  opalescent,  beads  a  little,  crazes. 
Cone  2 — Bright,  opalescent,  beads  a  little,  no  crazing. 


No.  14X.     Cone  03 :     Opalescent,  bright,  crazed  some,  no 

beading. 

Cone  01— Clear,  bright,  a  few  craze  marks,  no  bead- 
ing. 

Series  VI. 

In  both  the  cone  4  and  (>  l)urns  there  is  a  gradual 
gradation  in  this  series  from  IOC  to  10.  All  are  whiter  in 
the  cone  4  burn  than  in  the  cone  0  burn.  IOC  is  opalescent, 
blisters,  crawls  very  slightly,  has  no  crazing.  Whiteness, 
opacity,  crawling  and  crazing  increase  and  blistering  de- 
creases from  IOC  to  19.  No.  19  is  as  white  as  a  tin  enamel, 
though  some  beaded  and  crazed. 

Series  VII. 

No.  12C,    Cone  03 :    White,  opalescent,  tendency  to  bead, 

crazed. 

Cone  01 — Bright,  opalescent.  Beads  some,  crazes 
some. 


A    CHEAP    ENAMEL    FOR    STONEWARE.  26 

No.  20.     Cone  03 :     White,  opaque,  crawls  some,  blisters 

some,  crazed  a  little. 

Cone    01 — Translucent,    crawls    less,    blisters    some, 
crazes  less. 


No.  21.     Cone  03 :     AVhite,  opaque,  beaded  badly,  crazes 
badly. 
Cone  01 — White,  opaque,  beads,  crazes,  no  blistering. 


No.  22.      Cone   2:     White,   opaque,   beaded,   crazed   and 
blistered. 

Cone  4 — Blisters,  no  crazing  or  beading;  translucent. 
Cone  G — Opalescent,  blisters,  no  beading,  no  crazing. 


No.  23.    Cone  2  :    Blisters  slightly,  beads  and  crazes. 

Cone  4 — Blisters   slightly,   white,   no  crazing;  beads 
some. 

('one  (> — Opalescent,  blisters,  no  crazing  or  beading. 


No.  24.     ( -one  2 :     Badly  blistered,  slight  beading,  badly 
crazed. 
Cone  4 — Whitest  glaze  of  series.    Blisters,  no  crazing 


or  beading. 


(^one  6 — Appearance  same  as  in  cone  4  burn. 


Series  VIII. 

No.  14C.    Cone  03:    Opalescent,  crazes,  otherwise  good. 
Cone  01 — Same  as  the  cone  03  burn. 


No.  25.    Cone  03  :    Translucent,  crazes,  otherwise  good. 
Cone  01 — Opalescent,  smooth,  bright  and  crazed. 


26  A    CHEAP    ENAMEL     FOR     STONEWARE. 

No.  26.     Cone  03 :     Translucent,  whiter  than  25,  blisters, 

crazes. 

Cone  01 — Opalescent,     smooth,    bright    and     crazed. 
Slight  beading. 


No.  27.    Cone  03 :    Translucent,  whiter  than  26,  crazes,  no 
beading. 
Cone  01 — Translucent,  crazed  and  beaded. 


No.  28.    Cone  2 :    White,  opaque,  beaded  some,  crazed,  no 


blistering. 


Cone  4 — Blistered,  crazed,  no  beading. 

Cone  6 — Opalescent,  blistered,  no  crazing  or  beading. 


No.  29.     Cone  2 :     White,  opaque,  beaded,  blistered  some, 
crazed. 

Cone  4 — Blistered  badly,  crazed,  no  beading. 
Cone  6 — Blistered,  translucent,  no  crazing  or  beading. 

Series  IX. 

Cone  03 — This  series  has  given  the  best  results  so  far. 
All  are  white,  opaque,  though  crazed.  No.  30  quite  badly 
crazing  decreases  toward  No.  35  which  has  only  three  or 
four  craze  marks.  There  is  very  little  difference  in  this 
series  in  whiteness,  opacity  and  brilliancy.  The  glazes, 
however,  are  not  at  their  best,  a  little  higher  temperature 
would  improve  them.  None  are  blistered.  There  is  a  very 
slight  tendency  to  crawl  in  No.  30  which  appears  less  in  35. 

Cone  01 — All  the  members  of  the  series  are  beautiful 
opaque  glossy  enamels.  The  appearance  is  a  light  ivory  in 
color  and  texture.  No  evidence  of  blistering.  No.  30  is 
crazed  slightly ;  crazing  decreases  toward  35.  Nos.  34  and 
35  are  not  crazed  though  the  body  is  very  soft.  Trials  were 
also  taken  from  the  kiln  quite  hot.     There  is  a  \evy  slight 


A    CHEAP    ENAMEL    FOR     STONEWARE. 


27 


28  A    CHEAP    ENAMEL    FOR    STONEWARE. 

tendency  in  all  members  to  crawl  a  little  in  one  or  two 
small  spots  on  the  outside  rim  near  the  shoulder.  The 
insides  of  the  crocks  are  smooth  and  practically  flawless, 
aside  from  those  members  (Nos.  30,  31,  32,  and  33)  which 
crazed.  Brilliancy  and  opacity  equal  to  a  good  tin  enamel, 
color  very  nearly  as  good.  An  interesting  point  noticed 
both  in  the  cone  03  and  01  burns  is  that  the  tendency  to 
crawl  in  No.  35  containing  .55  AI2O3  is  less  than  in  No.  30 
containing  .40  AI2O3,  all  other  members  in  both  remaining 
constant.  The  crawling  tendency,  however,  is  no  greater 
than  that  of  many  good  stoneware  glazes  and  tin  enamels 
in  commercial  use  in  which  raw  borax  is  used  to  overcome 
that  trouble.  Therefore,  the  enamels  of  Series  IX  are  very 
promising,  since  they  contain  no  raw  borax  or  other  soluble 
salts. 

CONCLUSIONS. 

Series  I. 

In  this  series  ZnO  causes  greater  fusibility  than  BaO. 
Replacement  of  BaO  by  ZnO  reduces  crazing,  increases 
brilliancy  and  opacity. 

Series  II  and  III. 

The  use  of  bone  ash  direct  causes  flaking  of  the  glaze 
after  dipping.  Flaking  is  overcome  by  calcining  the  bone 
ash  with  flint. 

Replacement  of  CaO  from  whiting  by  CaO  from  bone 
ash  increases  refractoriness  materially  and  induces 
crazing. 

.131/3  P2^5  introduced  as  bone  ash  with  .3  ZnO  and 
.4  AI2O3  caused  no  beading  and  materiall}'  increased  AAliite- 
ness. 


A    CHEAP    ENAMEL    FOR    STONEWARE.  29 

Series  IV  and  V. 

The  use  of  raw  coleiiiaiiite*  in  glazes  causes  "powder- 
ing" before  a  dull  red  heat  is  reached.  Powdering  is  over- 
come by  using  dehydrated  colenianite. 

Replacement  of  bone  ash,  ZnO  and  SiOs  by  dehydrated 
colemanite,  materially  decreases  the  temperature  of  fusion, 
decreases  opacity  and  increases  brilliancy. 

The  opacifying  effect  of  colenianite  is  very  small,  pro- 
ducing at  best  onl}^  a  small  degree  of  opalescence. 

faeries  VT,  VII  and  VI IT. 

It  is  tlifticult  lo  determine  (he  action  of  aluminum 
phosphate  in  these  tliree  series.  Increasing  AI2O3  and 
P^.O.,  by  alnminum  plios])hate  increases  the  temperature 
of  fusion  a  little,  increases  whiteness  and  opacity. 

The  blistering  which  occin-s  has  the  appearance  of 
being  what  "single  fire"  enamel  brick  men  call  "steamed 
glazes.''  Opacity,  whiteness,  blistering,  beading  and  craz- 
ing generally  seem  to  be  lessened  by  increase  in  tempera- 
ture of  firing,  though  not  borne  out  in  all  cases.  None  of 
the  glazes  containing  aluminum  phosphate  are  good  enough 
for  commercial  use.  It  is  probable  that  more  consistent 
results  would  have  been  obtained  if  the  aluminum  phos- 
phate had  been  calcined  or  fritted. 

Series  IX. 

This  series  shows  that  good  glossy  enamels  are  possible 
as  low  as  cone  01  with  : 

2.5  Si02 


.2  ZnO 

.6  CaO 

.    .2  K2O 

\     .40    to     .55    AI2O; 

1     2.5    SlO: 
\       .2   P2O 

j      .8  B2O: 


*A  distinction  should  be  made  between  the  three  most  general  forms 
of  calcium  borate,  viz.,  colemanite,  priceite,  and  pandermite,  which  have 
different  physical  properties  such  as  hardness,  specific  gravity,  action 
before  the  blow  pipe,  etc.,  as  well  as  differences  in  their  respective  chemical 
analyses.  However,  both  priceite  and  pandermite  are  classed  as  "varieties'" 
under  colemanite  by  mineralogists. 


30  A    CHEAP    ENAMEL    FOR    STONEWARE. 

in  which  bone  ash  has  been  calcined  or  fritted  and  in  which 
the  excess  above  .3  AI2O3  is  added  as  calcined  clay. 

Experiments  with  bone  ash  as  an  opacifier  in  glazes 
are  not  new,  yet  the  author  fails  to  find  any  work  in 
ceramic  literature  pertaining  to  its  use  purely  as  a  glaze 
ingredient  aside  from  its  uses  in  glass  and  bone  china. 
The  question  has  been  raised  that  bone  ash  is  dangerous 
to  use  in  glazes  on  account  of  its  liability  to  cause  beading. 

It  is  a  well  known  fact  that  an  excess  of  the  opacifiers, 
alumina,  tin  oxide,  zinc  oxide  and  bone  ash  causes  beading. 
The  observations  of  the  writer  ]ead  him  to  believe  that  bone 
ash  has  no  greater  tendency  to  cause  beading  than  ZnO, 
SnOs  or  ALO...  If  we  attempt  to  add  bone  ash  to  a  ghizo 
of  the  Bristol  type,  which  is  already  loaded  up  with  an 
opacifier,  bringing  it  close  to  the  danger  point  of  beading, 
then  of  course  beading  will  occur. 

This  concludes  the  work  to  date.  The  next  step  will 
be  to  test  the  members  of  series  IX  for  range  of  tempera- 
ture to  determine  whether  they  are  suitable  for  commercial 
use.  If  so,  then  the  best  one  of  the  series  will  be  selected 
for  the  starting  point  of  series  X,  in  Avhich  the  BoOo  is  to 
be  gradually  replaced  by  SiOo  in  an  endeavor  to  produce 
suitable  "tinless"  enamels  for  higher  temperatures. 


THE  VISCOSITY  OF  CLAY  SLIPS. 

BY 

A.  V.  Bleixinger,  Chanipaia:n,  Illinois. 

The  plasticit3'  of  cla^'^  is  still  a  quality  \vliose  physical 
definition  has  not  yet  been  established,  though  many  at- 
tempts haye  been  made  to  do  so.  All  v;e  can  do  at  present 
is  to  continue  the  search  for  some  criterion  Ayhich  bears 
some  relation  to  this  elusiye  property.  Up  to  the  present 
such  i)ro]>erties  of  the  clay  as  the  tensile  strength,  both 
green  and  dry,  its  deformation,  cru.shing  strength  in  the 
green  state,  and  also  recently  the  yiscosity  imparted  to 
suspensions  of  clay  particles  haye  been  studied.  This  last 
[)roperty  is  promising  inasmuch  as  it  produces  a  plienonu^- 
non  Ayhich  is  clearly  not  shared  by  non-plastic  materials. 
hi  fact,  it  mighf  he  f<ai(l  that  clniis  are  rocks  ivhicJ>  iche)) 
puJvcrizcd  and  suspended  in  irater  itrodiiee  a  decided  in- 
crease  in  viscosity.^ 

This  yiscosity  is  cai»ab]c  of  being  expressed  numeri- 
cally with  a  degree  of  accuracy  \yhich  is  superior  to  that  of 
any  of  the  methods  mentioned  aboye. 

Siinonis^  has  measured  the  yiscosity  by  determining 
the  yolume  of  a  clay-slip  flowing  through  an  aperture  of 
2  mm.,  under  constant  pressure,  in  a  giyen  time.  A  mar- 
iotte  flask  was  used  to  maintain  constant  pressure  in  the 
burette  containing  the  slip.  The  burette  was  first  stand- 
ardized Ayith  water  and  the  relation  existing  between  the 
yolume  flowing  from  the  tube  and  the  pressure  obtained. 
This  relation  is  eyidently  A'^kp,  where  y=yolume  of  liquid 
discharged  in  a  giyen  time,  p=pressure  of  the  liquid  or  its 
height  in  the  yessel,  and  k^^coefificient  of  fluidity  or  the 

yiscosity.    Solying  for  k  we  obtain  k=^-p     If  now  the  pres- 
sures are  plotted  along  the  abscissa  and  the  yolumes  es- 


'Sprechsaal,  1905,  597. 

31 


32  THE  VISCOSITY   OF   CLAY    SLIPS. 

caping,   along   the  ordinate  we   obtain   for  ideal   liquids 

straight  lines  where  -^  is  equal  to  the  coeflQcient  of  fluidity 

represented  by  the  tangent  of  the  angle  made  by  the  line 
to  the  X  axis. 

In  the  case  of  da}'  slips  Simonis  found  the  relation  to 
be  not  so  simj^le  and  he  obtained  as  the  functions  of  vol- 
ume and  .pressure,  curves  of  higher  degree.  The  siiuie  in- 
vestigator, having  found  considerable  difficulty  witli  this 
method  in  working  thick  slips,  devised  a  second  method  for 
determining  the  cohesion  of  clay  slips  by  measuring  the 
weight  necessary  to  pull  away  a  5  cm.  glass  plate  from  the 
surface  of  the  liquid.  For  this  purpose  he  arranged  a  bal- 
ance, having  the  glass  disc  attached  at  one  end  of  the  beam 
and  a  scale  pan  at  the  other.  He  caused  very  fine  shot  to 
pour  onto  the  pan,  arranging  at  the  same  time  an  auto- 
matic shut-off  device.  Before  working  with  clay  slips  he 
determined  the  weight  necessary  to  pull  away  the  disc  from 
water.  Applying  the  test  to  cla^'  suspensions  and  noting 
the  weight  necessary  to  release  the  disc  he  subtracted  from 
this  load  the  weight  required  to  pull  away  the  glass  from 
water,  which  is  a  constant  factor.  In  this  way  the  cohesion 
value  of  the  clay  for  the  concentration  employed  Avas  de- 
termined. This  method  is  applicable  to  thick  slips  which 
fail  to  give  results  by  the  flow  method. 

There  are  faults  inherent  Avith  both  of  these  methods, 
the  flow  method  being  subject  to  irregularities  caused  by 
the  roughening  of  the  walls  of  the  A'essel,  the  irregular 
stopping  up  of  the  aperture  and  other  difficulties  while  the 
disc  method  is  faultv  as  soon  as  even  the  slightest  settling 
takes  place. 

In  looking  about  for  a  method  which  perhaps  might 
overcome  some  of  these  difficulties  the  Coulomb  method,  as 
employed  in  the  determination  of  the  viscosity  of  oils,  was 
considered  and  adopted.  Although  the  apparatus  as  de- 
signed is  not  suitable  for  thick  slips,  some  interesting 
results  were  obtained,  and  the  ease  and  accuracy  with 
which  the  viscosity  of  thin  slips  could  be  determined  makes 


THE  VISCOSITY   OF   CLAY    SLIPS. 


33 


34  THE   VISCOSITY   OF  CLAY    SLIPS. 

it  quite  suitable  for  certaiu  investigations.  It  lias  afforded 
tlie  writer  a  delicate  means  of  distinguishing  clays  of  dif- 
ferent plasticity,  or  of  following  the  effects  of  electrolytes 
and  organic  substances  upon  the  physical  character  of  the 
clay  suspensions. 

The  apparatus  itself  is  exceedingly  simple,  the  disc  being 
suspended  from  a  steel  wire  11  ft.  6  in.  long,  and  allowed 
to  rotate  within  a  vessel  filled  with  the  clay  slij),  figure  1. 
At  the  center  of  the  brass  disc  filled  with  lead,  a  rod  pro- 
jects, provided  with  a  clamp  for  gripping  the  wire  firmly. 
An  aluminum  pointer  is  fastened  to  the  rod  which  swings 
over  a  circular  scale  around  the  rim  of  the  receptacle,  grad- 
uated in  degrees.  This  scale  is  made  out  of  paper  and  var- 
nished. The  weight  of  the  disc  is  1333  grams  and  the 
thickness  of  the  wire  0.85  mm. 

In  making  the  test  the  slip  is  first  thoroughly  stirred 
up  and  poured  into  the  vessel.  The  disc  is  then  turned 
about  180°  by  means  of  the  pointer  and  released.  The  num- 
ber of  degrees  is  read  off  at  the  turning  point  of  the  vibra- 
tion so  that  the  amplitude  of  each  swing  in  the  same  direc- 
tion is  observed.  This  is  continued  until  several  readings 
have  been  taken.  The  disc  is  then  stopped  and  the  slip 
stirred  up  for  another  set  of  check  readings.  Tlie  ratio  of 
the  amplitude  of  two  successive  swings  is  obtained  by  di- 
viding the  first  reading  into  tlie  second,  the  second  into  the 
third,  and  so  on.  This  ratio  is  a  constant  for  the  same  slip 
at  the  same  temperature.  It  is  important  to  make  note  of 
the  temperature,  or  better  to  keep  it  constant,  since  the 
viscosity  of  the  water  itself  changes  with  change  in  tem- 
perature. 

The  time  of  periodic  vibration  is  obtained  h\  taking 
the  total  of,  say,  ten  complete  vibrations  and  dividing  by 
20.  It  may  also  be  calculated  from  the  length  of  the  wire. 
For  the  apparatus  in  question  the  periodic  time  of  vibra- 
tion was  found  to  be  3.6  seconds,  thus  enabling  two  ob- 
servers to  make  the  readings  quite  readily. 

Knowing  the  period  of  oscillation  and  the  ratio  of  the 
amplitudes  we  can  calculate  the  viscosity  of  water  and  that 


THE   VISCOSITY   OF   CLAY    SLIPS.  35 

of  the  slips  to  be  compared  with  it.  In  this  work  the  vis- 
cosity of  water  is  always  used  as  the  standard,  and  hence 
the  viscosities  obtained  are  in  terms  of  the  viscosity  of 
water. 

Several  methods  of  calculation  might  be  employed, 
based  upon  the  laws  of  the  dampenino-  of  vibrations.  As- 
suming for  instance  that  the  ratio  of  the  amplitudes  is  O.S 
and  the  time  is  1.5  seconds  for  each  vibration,  we  obtain  as 
an  expression  for  the  viscosity  of  the  liquid  : 

0.8=e-i  5k  or 

—log  0.8=1.5k  log  e. 

Then  K==^?^-' =0.15 

1.5  log  e 

If  in  another  slip  the  ratio  of  the  amplitudes  is  found 
to  be  equal  to  0.7  and  solving  again  for  K  Ave  obtain  0.24. 
The  viscosities  of  the  two  liquids,  therefore,  are  to  each 
other  in  the  ratio  of  15:  24.  A  somewhat  sim]»ler  relation 
might  be  used  for  determining  the  relative  though,  of 
course,  not  the  absolute  viscosities,  in  which 

Vi=coefficient  of  viscosity  of  one  liquid: 

i'j=rratio  of  the  amplitudes  of  any  two  successive  os- 
cillations in  the  same  direction  in  the  same  liquid  ; 

Ti=period  of  oscillation ; 

di=dampening  constant. 

Similarly  let  V2,  r^,  T^  and  d^  be  the  corresponding 
values  for  the  second  liijuid.    We  have  then  the  relation 

di     To  log  Tj     Vi 
do     Ti  log  ro     Vo 

This  gives  us  K,  a  coefiicient  of  specific  viscosity.  The 
standard  employed  is  distilled  water  whose  ratio  is  de- 
termined at  the  same  temperature  as  the  ratio  of  the  slips 
to  be  tested.  The  constant  for  water,  of  course,  differs  with 
different  apparatus.  In  the  experiments  carried  on  in  the 
apparatus  described  it  was  0.89. 

It  was  decided  to  make  viscosity  determinations  with 
three  kaolins  which  differ  widely  in  their  physical  behavior. 


36 


THE   VISCOSITY   OF   CLAY    SUPS. 


The  method  obviously  is  not  intended  for  clays  which  are 
coarse-grained,  and  if  they  are  to  be  tested  in  this  way  the 
coarser  portion  must  be  screened  off.     The  three  clays  se- 


TRANS.  AM.  CER.  50C  .  VOLX 


Bl_E.I(MIN&ER 


II 
|a.o 

1.9 

O 

/.6 

Si.. 


1.4 


,/.3 


<«  1.2. 
o 

."^    i.l 


1.0 


t 

o^)^4o 

7.~ 

TenaBallC 
T=I9»C, 

F 

:.-,i 

/ 

/ 

/ 

/ 

/ 

Flor 
T=2I 

idaK 

°C 

aoliny 

/ 

J 

> 

/ 

/ 

> 

/ 

y 

X' 

x 

N.C.K 

ao\\n, 

^^ 

-'^i        "^^ 

94^ 

"     " 

, 

— ■ — ^ 

3       4        5       6        7        8        9 
Percent  oSClaij    By  Weight. 


10       U       \Z      »3      i4      /5 


THE   VISCOSITY   OF   CLAY    SLIPS.  37 

lected  were  the  Xortli  Carolina  kaolin,  Florida  kaolin,  and 
the  Tennessee  ball  clay,  Xo.  7. 

The  c-lavs  were  wei<j;hed  out,  the  moisture  factor  being- 
allowed  for,  and  mixed  with  a  weighed  amount  of  distilled 
water.  The  mixing  was  done  in  a  small  gallon  porcelain 
ball  mill,  it  being  run  for  forty  minutes  in  each  case.  The 
heaviest  slip  employed  consisted  of  85%,  by  weight,  of 
water  and  15%  of  clay,  the  apparatus  not  being  able  to 
vibrate  in  thicker  slips.  The  15%  slip  was  at  tirst  blended 
with  a  1%  suspension  for  the  intermediate  compositions, 
but  later  the  heavier  slip  was  diluted  with  the  distilled 
water  alone.  The  blending  was  accomplished  by  siinply 
stirring  in  a  pitcher.  In  Fig.  2  will  be  found  the  viscosit}' 
curves  of  the  three  clays  for  different  concentrations.  They 
were  the  average  of  30  determinations  in  each  case,  and  the 
readings  showed  a  variation  of  about  ±  2%.  It  will  be 
observed  that  at  first  the  viscosity  was  decreased,  a  fact 
which  is  quite  interesting.  The  Florida  kaolin  occupies  a 
position  midway  between  the  North  Carolina  kaolin  and 
the  ball  clay,  but  nearer  to  the  kaolin  than  to  the  latter. 

Might  it  not  be  possible  that  by  this  or  other  viscosity 
measurements  we  shall  be  enabled  to  correlate  or  classify 
our  plastic  clays?  The  practical  potters  constantly  call 
our  attention  to  the  fact  that  we  disregard  the  physical 
properties  of  kaolins,  and  that  in  our  ceramic  schools  we 
do  not  properly  discriminate  in  their  use  in  our  experi- 
ments. It  is  our  duty  therefore  to  employ  such  means  as 
these  to  help  them,  as  well  as  to  push  forward  our  knowl- 
edge of  the  elusive  properties  of  clays. 

As  has  been  said,  this  apparatus  is  very  delicate,  and 
such  things  as  the  use  of  hydrant  water  in  place  of  the 
distilled  will  cause  marked  changes  in  the  behavior  of  the 
clays.  This  naturally  leads  to  the  action  of  salts  like 
sodium  carbonate,  sodium  silicate,  etc.,  which  opens  up  a 
large  field  of  experimentation. 

The  work  is  to  be  continued  with  a  modified  apparatus 
which  it  is  intended  to  operate  in  heavier  slips. 


NOTE  ON  SOME  FUSION  CURVES. 

BY 

A.  V.  Bleininger_,  Champaign,  111. 

In  the  study  of  the  chemistry  and  physics  of  ceramics 
the  mechanism  of  the  fusion  processes  is  of  vital  import- 
ance. Yet  our  knowledge  of  these  fundamental  processes 
is  exceedingly  limited,  which  is  due  to  the  fact  that  we 
have  continued  to  investigate  complex  conditions  with  so 
many  variables  that  our  equations  have  been  far  too  few 
to  solve  them.  It  is  high  time  that  we  modestly  begin  the 
study  of  the  simpler  relations  and,  after  mastering  them, 
proceed  to  the  investigation  of  the  more  complicated  sa's- 
tems.  There  is  no  reason  why  in  this  way  we  should  not 
obtain  in  time  a  fairly  accurate  knowledge  of  the  chemistry 
of  clays. 

We  must  expect  to  meet  discouragement,  howtver,  for 
only  by  the  most  painstaking  care  in  keeping  the  conditions 
constant  will  we  be  enabled  to  obtain  consistent  results. 
We  must  at  all  times  remember  that  the  reactions  taking 
place  in  our  clays  are  never  completed  but  will  always 
remain  far  from  the  end-point,  and  that  they  are  dependent 
upon  the  conditions  of  the  partial  ecjuilibrium  reached.  Ev- 
idently important  factors  are, — slow  or  rapid  heating,  crys- 
talline or  amorphous  substances,  etc. 

Though  we  may  not  reach  the  most  exact  knowledge 
of  the  subject,  by  keeping  as  many  conditions  constant  as 
possible  we  shall  learn  much  from  the  correlation  of  melt- 
ing-points and  here,  fortunately,  the  ditferentiation  of 
melting  point  series  is  of  greater  help  to  us  ihan  the 
knowledeg  of  isolated  melting  points.  In  this  way  the 
maximum  and  minimum  points  are  detected,  and  we  are 
enabled  to  fix  the  temperatures  at  which  chemical  reactions 
take  place,  the  fusion  temperatures  of  the  eutectic  mixtures 

39 


40 


NOTE    ON    SOME    FUSION    CURVES. 


and  the  compositions  corresponding  to  these  critical 
points.  Usually,  maximum  points  correspond  to  com- 
pounds and  tlie  minimum  points  to  eutectic  mixtures. 

In  the  preliminary  study  of  the  fusion  curves  begun  at 
the  University  of  Illinois,  the  first  work  comprised  mix- 
tures of  feldspar,  ferric  oxide  and  whiting,  since  tliese 
mixtures  are  of  interest  in  the  study  of  some  of  the  Illinois 
clays.  Commercial  materials  were  used  and  it  was  found 
that,  thougli  the  whiting  appeared  to  be  of  good  color  and 
A\as  bought  as  liigh-grade  material  it  proved  quite  impure. 

The  composition  of  the  feldspar,  whiting  and  ferric 
oxide  was  found  to  be  as  follows : 


Ferric 
Oxide 


I 
Lime        Magnesia 


Feldspar    I  68.22  I   17.83      trace 

Whiting    I      1.62   I     3.50  I   trace 

Iron  Oxide   |    |    99.00 


0.30 
52.65 


O.II 

trace  ' 


12.13 


1.90 


These  tluee  constituents  were  ground  together,  dry, 
in  a  small  ball  mill,  in  various  proportions,  from  100% 
feldspar  to  407c  ferric  oxide,  100%  spar  to  40%  whiting 
and  100%  spar  to  40%  ferric  oxide  plus  whiting,  in  inter- 
vals from  l-57f .  The  interval  was  made  small,  close  to 
10090  of  feldspar,  so  as  to  bring  out  the  eft'ect  of  smaller 
amounts  of  either  material  upon  feldspar.  From  17'  the 
interval  was  increased  to  2,  3  and  5%  as  the  feldspar 
diminished  in  amount. 

The  nuxtures  were  then  made  up  with  dextrine  water 
into  a  dougli  and  molded  into  cones  in  a  metal  mold.  .After 
drying,  tlie  cones  were  placed  on  clay  slabs,  in  duplicate 
rows  and  melted  down  in  a  coke-fired  test  kiln,  having  been 
protected  from  the  flame  by  means  of  a  high  tiU^  sagger 
which  was  partially  open  on  the  back  and  front.  A  thermo- 
couple was  placed  as  close  to  the  cones  as  possible.  Cor- 
rection was  made  for  the  cold  junction  temperature. 
Through  a  thin  piece  of  glass  inserted  in  the  spy  hole  the 
cones  were  watched  with  ease,  and  their  going  down  ob- 


NOTE    ON    SOME    FUSION    CURVES. 


41 


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3^niVy3dN3± 


42  NOTE    ON    SOME    FUSION    CURVES. 

served  by  means  of  an  opera  glass.  Unfortunately  some  of 
the  cones  Avere  cracked  in  drying  due  to  an  excess  of  dex- 
trine and  broke  off  in  the  kiln.  These  were  not  considered 
in  the  result. 

In  Fig.  1  we  have  shown  the  fusion  curve  of  the  feld- 
spar-ferric oxide  series,  and  a  eutectic  is  clearly  indicated 
with  91%  feldspar  and  9%  of  iron  oxide.  This  mixture 
corresponds  to  the  formula  : 

0.015  MgO 
0.034  CaO 
0.766  K,0 
0.185  ^'aoO 

The  feldspai-  formula  is  represented  by  the  same  for- 
mula but  without  the  iron.  This  mixture  therefore  fuses 
at  a  lower  temperature  than  the  feldspar  itself  or  any 
other  mixture  of  the  series. 

In  Fig.  2  the  feldspar-lime  series  is  not  complete  owing 
to  the  breaking  of  some  of  the  cones,  and  hence  the  eutectic 
point  is  not  definitely  established,  but  it  is  quite  evident 
that  it  is  close  to  97 7^  feldspar,  S^c  whiting.  This  would 
correspond  to  a  slight  enriching  of  the  spar  in  lime 
corresponding  to  about  0.03  equivalent.  Since  this  point 
was  not  determined  with  certainty  no  interest  is  attached 
to  its  formula. 

In  Fig.  3  there  are  plotted  the  compositions  of  the 
mixtures  in  terms  of  the  percentages  of  feldspar,  iron-oxide 
and  whiting,  and  it  is  evident  that  the  isothermal  composi- 
tions are  connected  by  some  definite  law.  Each  curve 
represents  a  temperature  interval  of  20°,  correspond- 
ing to  the  range  of  one  cone.  Thus  every  mixture  in  the 
inner  area  melted  between  1175°  and  1195''C.  The  increase 
in  area  indicates  the  enriching  of  the  fusion  by  the  solution 
of  other  materials  on  raising  the  temperature,  and  ^^e 
learn  thus  in  what  direction  this  takes  place. 

Similar  curves  carried  on  very  carefully  with  pure 
lead  silicates,  fusing  the  cones  in  an  electric  furnace, 
showed  some  disturbing  factor  owing  to  volatilization  of 
the  lead,  and  hence  are  not  produced.     This  trouble  was 


XOTE   ON    SOME    FUSION    CURVES. 


43 


,  TRANS.   AM   CER.  SOC      VOL 


BLEININCER 


1200 


Q!:|150 


MOO 


FIG  2.. 

FUSION    CURVE 
FELDSPAR-LIME  SERIES. 

- 

"\ 

. 

/ 

1 

/ 

1 

0   WHITING 
100    FELDSPAR 


5  10 

55  90 

°iO    COMPOSITION 


15 
85 


TRANS     *vi    CtR    SOC     VOL 


PIG  3 


BLEINlNGEf^. 


44  NOTE    ON    SOME    FUSION    CURVES. 

encountered  even  with  fritted  glasses,  and  the  work  is  to 
be  rejieated  under  speeial  precautions. 

DISCUSSION. 

77?c  Chair:  I  think  Professor  Bleininger  has  given 
us  a  splendid  paper,  and  I  am  very  glad  to  know  that  he 
is  getting  near  to  the  practical  man.  I  will  call  on  Mr. 
Stover,  as  a  practical  man,  to  discuss  the  paper. 

Mr.  I^torer:  I  would  like  to  ask  Professor  Bleininger 
why  he  expressed  the  data  in  percentage  weights? 

Mr.  Blciiiiiifjcr:    Because  it  was  the  simplest  way. 

.1//".  ^Stovcr :  I  don't  want  to  say  a  word  against  the 
use  of  technical  formulae,  for  I  sat  up  many  nights  in  order 
to  master  it  so  I  could  figure  them  out  by  myself;  but  it  is 
a  fact  that  I  have  been  arguing  along  the  line  of  this  sort 
of  expression  without  much  result  until  at  this  meeting. 
I  have  contended  it  would  make  it  more  simple,  and  if  we 
could  have  the  kind  of  data  Mr.  Bleininger  has  been  trying 
to  give  us  lying  around  in  the  mixing  room^i  of  the  practical 
potters  in  Trenton  and  East  Liverpool,  we  wouhl  have 
something  here  in  the  pages  of  the  proceedings  which  would 
be  of  practical  value.  But  for  the  most  part,  we  are  soaring 
around  ovei*  their  heads  and  they  cannot  understand  us. 
I  am  glad  Professor  Bleininger  has  put  bis  data  in  plain 
percentages,  for  T  believe  it  will  be  productive  of  practical 
results. 

lite  Cliair:  I  want  to  say,  as  a  practical  man,  that  I 
am  impressed  witli  the  fact  that  we  are  getting  closer  and 
closer  to  the  practical  man  in  our  work.  There  are  many 
things  about  the  technical  part  of  the  American  Ceramic 
Society's  work  which  the  practical  man  cannot  understand  ; 
but  he  realizes  the  meat  is  there  even  though  he  cannot 
always  digest  it.  I  think  this  is  a  simple  method  and  that 
the  practical  man  will  by  and  by  conclude  that  after  all 
there  is  something  in  pottery  worth  knowing  that  he  does 
not  understand. 


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